Multiple organ dysfunction (MOD) is the leading cause of mortality in septic patients with circulatory shock. Recent evidence suggests that the overproduction of the cytokine, tumor necrosis factor-alpha(TNF), and oxygen free radical molecules may mediate the progression of sepsis to MOD and death. In this study, we have examined the ability of MDL 101,002, a free radical scavenger, to reduce organ dysfunction and cytokine secretion induced by lipopolysaccharide (LPS) administration in rats. Treatment with MDL 101,002(10-60 ng/kg, i.p.) 30 min prior to an LPS challenge resulted in a dose-dependent reduction in several markers indicative of organ dysfunction and mortality. MDL 101,002 markedly decreased LPS-induced liver and kidney damage as indicated by serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) or urea and creatinine, respectively. MDL 101,002 also prevented LPS-induced pulmonary edema, but did not prevent leukopenia and only partially reduced thrombocytopenia. Associated with these improvements in organ dysfunction and survival was a modest decrease in LPS-stimulated interleukin-1 alpha (IL-1 alpha) and interleukin-1 beta (IL-1 beta) secretion and a marked ( > 90%) inhibition of TNF secretion by MDL 101,002. The data are consistent with a role for oxygen free radicals in the development of endotoxin-induced organ dysfunction and shock and suggest that free radical scavengers could reduce the mortality consequent to sepsis by decreasing organ dysfunction, at least in part, through a reduction in free radical stimulated cytokine secretion.

Angiotensin converting enzyme (ACE) and neutral endopeptidase (NEP), are two mechanistically similar enzymes involved in the metabolism of several vasoactive peptides. Selective inhibitors of ACE are effective antihypertensive agents in high-renin, renovascular rats and normal-renin, spontaneously hypertensive rats (SHR), but are not effective in the low-renin, deoxycorticosterone acetate (DOCA)-salt hypertensive rats. In contrast, NEP inhibitors are only effective in the low-renin model of hypertension. Treatment with a combination of selective inhibitors or with a dual inhibitor of both enzymes produces an antihypertensive response regardless of basal plasma renin activity. In this study, we compared the activities of MDL 100,173, a novel subnanomolar inhibitor of both ACE and NEP, with those of equimolar doses of captopril, a selective ACE inhibitor, following intravenous administration in these three rat models of hypertension. Treatment with MDL 100,173 significantly lowered blood pressure compared to vehicle treatment in all three models, whereas captopril treatment lowered blood pressure in the renovascular and SHR models only. Administration of MDL 100,173 also significantly elevated diuresis and natriuresis compared to either vehicle or captopril treatment in the SHR and DOCA-salt rats. Urinary excretion of atrial natriuretic peptide (ANP) was increased by MDL 100,173 treatment in all three models of hypertension. Treatment with captopril did not alter urine, sodium, or ANP excretion in any of the models. However, plasma-renin activity was elevated by both MDL 100,173 and captopril '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ''''''''

Evidence of a role for oxygen-derived free radicals in the pathophysiology of endotoxic shock has been found in animal models. However, the importance of free radicals in chronic models of bacterial infection has not been examined. In this study a novel nitrone radical spin trap is described and its activity in animal models of endotoxic shock and chronic bacteremia were explored. MDL 101,002 is a cyclized variant of alpha-phenyl N-tert-butyl nitrone (PBN), an established spin trap. MDL 101,002 can react with free radicals to form persistent adducts as demonstrated by electron paramagnetic resonance (EPR) spectroscopy. This agent is about 10 times more potent than PBN as an in vitro antioxidant and scavenger of hydroxyl radicals. In a rat endotoxic shock model MDL 101,002 (3-30 mg/kg, i.p.) administered 30 min prior to endotoxin (30 mg/kg, i.p.) treatment reduced mortality in a dose-dependent manner. Peroxide-enhanced chemiluminescence in hepatic homogenates from endotoxin treated rats was elevated indicating that oxidative stress and antioxidant depletion was increased. Importantly, treatment with MDL 101,002 (30 mg/kg, i.p.) 30 min prior to, and 120 min following endotoxin, minimized the increase in chemiluminescence. MDL 101,002 also reduced mortality in a model of chronic bacteremia employing implantation of infected fibrin clots into the peritoneal cavity of gentamicin-treated leukopenic rats. MDL 101,002 (2.5 mg/kg/hr) increased survival from 24% to 52% in these rats. These data are consistent with a role for free radicals in the pathophysiology of endotoxic shock and suggest free radicals are also important mediators in chronic models of sepsis.